Lead-free copper alloy and component with the lead-free copper alloy

ABSTRACT

A lead-free copper alloy has from 70.0 to 83.0% by weight of Cu, from 2.0 to 2.9% by weight of Si, from 0.05 to 0.10% by weight of P, from 0.01 to &lt;0.30% by weight of Sn, and a balance of Zn and unavoidable impurities. The lead-free copper alloy is particularly suited for the production of an installation components for conducting drinking water.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority, under 35 U.S.C. § 119, of German patent application DE 10 2020 127 317.7, filed Oct. 16, 2020; the prior application is herewith incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a lead-free copper alloy.

Copper alloys with Sn and Al are known from the prior art. In addition, Zr is necessarily alloyed into these to effect grain refinement. Such copper alloys are described, for example, in European patents Nos. EP 1 777 305 B1, EP 1 502 964 B1 and EP 1 777 308 B1.

German patent DE 103 08 778 B3 discloses a lead-free copper alloy which can be employed in the field of mains water and sanitary installation. That copper alloy necessarily contains Fe and/or Co and also Ni and Mn.

A similar alloy is known from European published patent application EP 1 600 515 A2.

European published patent applications EP 1 600 516 A2, EP 1 559 802 A1, EP 1 600 517 A2, EP 1 045 041 A1 and EP 1 508 626 A1 each disclose lead-free copper alloys in which the content of Sn is at least 0.3% by weight. The content of Al is at least 0.1%.

In practical use, the above-mentioned lead-free alloys do not always form a sufficiently corrosion-inhibiting covering layer or oxide layer on contact with mains water. This results in undesirable corrosion caused by selective leaching of Zn from the alloy (known as “dezincification”).

BRIEF SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide an alloy which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which provides for a lead-free copper alloy whose corrosion resistance is improved, particularly when the alloy is used in mains water technology.

With the above and other objects in view there is provided, in accordance with the invention, a lead-free copper alloy comprising from 70.0 to 83.0% by weight of Cu, from 2.0 to 2.9% by weight of Si, from 0.05 to 0.10% by weight of P, from 0.01 to <0.30% by weight of Sn, balance: Zn and unavoidable impurities.

The proposed lead-free copper alloy displays improved corrosion resistance, in particular on contact with drinking water (i.e., mains water). The improved corrosion resistance is attributed to the formation of a covering layer or oxide layer having improved adhesion. Improved adhesion is surprisingly achieved even at a content of Sn of less than 0.30% by weight. In addition, it has been found that the corrosion resistance can be increased by addition of surprisingly even less than 0.1% by weight of Al.

The content of Cu is advantageously from 73.3 to 76.8% by weight.

In an advantageous embodiment, the copper alloy of the invention comprises from 0.01 to <0.1% by weight of Al. The proposed addition of Al improves the adhesion of the covering layer.

In a further embodiment, the proportion of Si is from 2.40 to 2.90% by weight, preferably from 2.60 to 2.80% by weight, advantageously from 2.60 to 2.78% by weight. The proposed addition of Si contributes to a reduction in the amount of kappa phase to a proportion of not more than 25% by weight. It has been observed that the reduction in the proportion of the kappa phase contributes to an improved corrosion resistance. The proportion of kappa phase is preferably not more than 25% by weight, in particular from 5 to 20% by weight.

In a further embodiment, the proportion of Al is advantageously from 0.01 to 0.05% by weight. Furthermore, the proportion of P can be from 0.08 to 0.10% by weight. The proposed proportions make it possible to produce a particularly corrosion-resistant alloy.

The proposed lead-free copper alloy is particularly suitable for producing installation components for the mains water sector, for example for the production of fittings, valves, pipes and the like.

Working examples of the invention will be explained in more detail below with the aid of experimental results.

Table 1 shows the composition of experimental alloys.

TABLE 1 Alloy elements (% by weight) Alloy No. Cu Si P Sn Al 2737 76.43 3.35 0.091 0.003 0.002 2838 76.42 3.02 0.091 0.003 0.002 2839 76.45 2.72 0.091 0.003 0.001 2840 75.99 2.73 0.093 0.003 0.001 2841 76.44 2.75 0.052 0.002 0.001 2842 76.46 2.71 0.09 0.103 0.001 2843 76.52 2.71 0.093 0.287 0.001 2845 76.33 3.1 0.092 0.019 0 2846 76.16 3.4 0.048 0.005 0 2858 76.6 2.61 0.095 0.288 0.042

To produce the experimental alloys set forth in Table 1, test specimens were produced as follows:

A melt formed by the alloy elements was poured at a temperature of from 1020° C. to 1050° C. into sand molds having a diameter of 40 mm. The solidified test specimens were then turned to a diameter of 24 mm. The diameter of the test specimens was then reduced to 8 mm by an extrusion simulation at a temperature of 700° C. The test specimens were finally heat treated at from 550° C. to 580° C. for 2 hours and then cooled in air.

In Table 1, the alloys Nos 2842, 2843 and 2858 correspond to alloys according to the invention. The remaining alloys are comparative alloys.

Table 2 shows results of microstructural analyses.

TABLE 2 Microstructure Alloy elements Kappa Gamma Alloy No. Cu Si P Sn Al MK MK 2737 76.43 3.35 0.091 0.003 0.002 44% 1% 2838 76.42 3.02 0.091 0.003 0.002 31% 1% 2839 76.45 2.72 0.091 0.003 0.001 22% 1% 2840 75.99 2.73 0.093 0.003 0.001 24% 1% 2841 76.44 2.75 0.052 0.002 0.001 19% <1%  2842 76.46 2.71 0.09 0.103 0.001 15% 1% 2843 76.52 2.71 0.093 0.287 0.001 16% 1% 2845 76.33 3.1 0.092 0.019 0 26% <1%  2846 76.16 3.4 0.048 0.005 0 42% <1%  2858 76.6 2.61 0.095 0.288 0.042 10% <1% 

The inventive alloys Nos 2842, 2843 and 2858 display a low content of kappa phase (=kappa MK) of from 10 to 16% by weight.

BRIEF DESCRIPTION OF THE DRAWING

The single FIGURE of the drawing is a column chart showing the dezincification of three novel allows compared with a prior art alloy.

DESCRIPTION OF THE INVENTION

The single FIGURE shows the maximum depth of dezincification [μm] for the three alloys according to the invention, Nos. 2842, 2843 and 2858, compared with the alloy No. 2846 (prior art). The “maximum depth of dezincification” is the depth up to which leaching of Zn was detectable according to the following experimental procedure.

The specimens were sawn. The sawn surface was brought into contact with mains water for a period of 8 weeks. The mains water was changed twice per week. The hardness of the mains water was set to a value of 25° dH by the addition of NaCl and MgSO₄. The chloride content was 250 mg/l, and the content of sulfate was likewise 250 mg/l. The leaching experiment took place under room conditions.

To determine the depth of dezincification, the specimen was cut perpendicular to the surface, polished and then optically analyzed under a reflected light microscope. The depth of dezincification could be seen from the characteristic color of the zinc-free copper sponge.

The addition of Al leads to increased oxide formation. Even small amounts of aluminum (from 0.04% by weight upwards) surprisingly display firmly adhering oxide layers in a scale test (heat treatment at 800° C.) compared to aluminum-free specimens in the case of which the oxide layer flakes off severely. A protective effect is generally attributed to the oxide. The better the oxide adheres, the better the protective effect.

As can be seen from the FIGURE, the novel alloys Nos 2842, 2843 and 2858 according to the invention have a drastically decreased maximum depth of dezincification compared to the alloy No. 2846 (prior art). Especially in the case of the inventive alloy No. 2843, no dezincification could be observed.

The alloy according to the invention displays a drastically improved corrosion resistance on contact with mains water. 

1. A lead-free copper alloy, comprising: a content of from 70.0 to 83.0% by weight of Cu; a content of from 2.0 to 2.9% by weight of Si; a content of from 0.05 to 0.10% by weight of P; a content of from 0.01 to <0.30% by weight of Sn; and balance Zn and unavoidable impurities.
 2. The lead-free alloy according to claim 1, wherein the proportion of Cu is from 73.3 to 76.8% by weight.
 3. The lead-free copper alloy according to claim 1, which further comprises a content of from 0.01 to <0.1% by weight of Al.
 4. The lead-free copper alloy according to claim 1, wherein a proportion of Si is from 2.40 to 2.90% by weight.
 5. The lead-free copper alloy according to claim 4, wherein the proportion of Si is from 2.60 to 2.80% by weight.
 6. The lead-free copper alloy according to claim 4, wherein the proportion of Si is from 2.60 to 2.78% by weight.
 7. The lead-free copper alloy according to claim 1, comprising a proportion of kappa phase of not more than 25% by weight.
 8. The lead-free copper alloy according to claim 1, further comprising a content of Al in a proportion of from 0.01 to 0.05% by weight.
 9. The lead-free copper alloy according to claim 1, wherein a proportion of P is from 0.08 to 0.10% by weight.
 10. A component, comprising the lead-free copper alloy according to claim
 1. 11. The component according to claim 10, configured for use in an installation for a mains water sector. 